Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $237.85   9.564%   $260.598   $260.60   $260.60   $260.60  
  Purchase #2 $194.35   11.437%   $216.5778   $216.58   $216.60   $216.60  
  Purchase #3 $165.90   7.234%   $177.9012   $177.90   $177.90   $177.90  
  Purchase #4 $14.93   8.332%   $16.174   $16.17   $16.15   $16.20  
  Purchase #5 $152.69   13.776%   $173.7246   $173.72   $173.70   $173.70  
  Purchase #6 $118.82   10.308%   $131.068   $131.07   $131.05   $131.10  
  Purchase #7 $93.37   5.437%   $98.4465   $98.45   $98.45   $98.40  
  7 purchase totals = $977.91       $1,074.4901   $1,074.49   $1,074.45   $1,074.50